Plasma processing is widely used in the semiconductor industry for deposition, etching, resist removal, and related processing of semiconductor wafers and other substrates. Plasma sources (e.g., microwave, ECR, inductive, etc.) are often used for plasma processing to produce high density plasma and reactive species for processing substrates.
One type of process carried out in the past using plasma is atomic layer etching. Atomic layer etching is a technique to perform critical etching with very fine precision for semiconductor device manufacturing. Atomic layer etching is performed on a thin layer while attempting to avoid undue sub-surface damage or undesirable modifications. Atomic layer etching may be performed to etch a very thin layer that overlays another critical layer. Atomic layer etching may also be employed at the end of an etch process for removing minor amounts of a remaining layer that was previously etched without damaging the underlying structures. It is desired to use atomic layer etching to have self-surface limited process reaction so uniformity is controlled by surface exposure only, not controlled by plasma uniformity anymore so the etch amount uniformity can be further improved.
In the past, atomic layer etching methods included first a surface reactive species attachment step followed by plasma ion bombardment to remove the reactive surface layer. Such ion bombardment control is only one aspect of the possible approach for the atomic layer etching. Traditional atomic layer etching has been very successful on films containing silicon, such as Si, Si3N4 or SiO2. The above traditional method using ion bombardment activation, however, has not been successful on other layers, particularly layers containing carbon and other low dielectric films. These other materials, for instance, are less reactive to the ion bombardment and more to the chemical reaction. Further, in some embodiments, higher temperatures are needed in order for the etching process to occur which can result in very long etching cycles that provide little control over the process.
Consequently, a need exists for an etch method for etching carbon containing films and other similar films including films having a low dielectric constant. More particularly, a need exists for a method and process for performing an atomic layer etching process on the above materials.